PHOTOELECTROCHEMICAL PROPERTIES OF INDIUM DOPED IRON-OXIDE

Oxygen photoanodes formed by reactive sputtering of iron oxide onto conducting indium tin oxide (ITO) substrates held at 350 ° C have been investigated by conventional photoelectrochemical, impedance, XPS and auger spectroscopic methods. This fabrication procedure leads to films containing 8 to 20 atomic % indium in the front portion of the film, increasing to much higher values near the ITO interface (back portion of the film). Two interesting effects are observed with the thin-film iron oxide formed in this way. The first is that the as formed films must be vacuum annealed before an appreciable dc photoanodic response is observed. Secondly, films 250 nm thick display the property of giving about double the quantum yield for back face, than for front face, illumination over the spin and parity forbidden transition centered at 535 nm. On correcting for transmission and reflection losses, the resulting true quantum efficiencies satisfy the same inequality, a result that can only be accounted for by a higher ( > 2 × ) primary quantum efficiency for the back, versus the front portion of the film. As these films show substantially higher quantum efficiencies than do indium free films of the same thickness, it is concluded that the indium in the films is responsible for the increase in primary quantum efficiency. This result is discussed in terms of a localized states model for α-Fe2O3. © 1990.